1. Field of the Invention
The present invention relates to a wire bonding apparatus and more specifically to an improved tension applying means which applies a constant tension to the wire in the wire bonding apparatus.
2. Prior Art
Conventional examples of tension applying means used in wire bonding devices are disclosed in Japanese Patent Application Publication (Kokoku) Nos. 53-9949 (called "Conventional Example 1"), 53-10425 (called "Conventional Example 2"), and 61-41231 (called "Conventional Example 3"). FIG. 5 illustrates Conventional Example 1, FIG. 6 illustrates Conventional Example 2 and FIG. 7 illustrates Conventional Example 3.
Conventional Examples 1 through 3 all include nozzles 1 each having a nozzle hole 1a that blows out a gas and two gas guide plates 2 and 3 which are installed along the direction of flow of the gas blown out of the nozzle 1. In Conventional Example 1, ducts 5 are formed in the gas guide surfaces 4 of the two gas guide plates 2 and 3. The cross sections of these ducts 5 becomes wider toward the nozzle 1 and narrower away from the nozzle 1.
In Conventional Examples 2 and 3, the gas flows between the two gas guide plates 2 and 3. Accordingly, as shown in FIG. 8, the gas 6 can be pushed out in the direction of width of the gas guide plates 2 and 3 (i.e., in the direction perpendicular to the direction of the center line of the nozzle 1). Thus, the gas is not stable in the direction of blowing. As a result, the bonding wire 7 is caused to swing violently in the direction of width of the gas guide plates 2 and 3 so that the wire 7 is applied with stress, which is not desirable. Furthermore, since the wire 7 swings violently in the direction of width of the guide plates 2 and 3, the paying out of the wire from the spool is not accomplished smoothly.
In addition, since two gas guide plates 2 and 3 are used in Conventional Examples 1 through 3, contamination of the inside surfaces of the gas guide plates 2 and 3 cannot easily be observed, and the gas guide plates 2 and 3 are not cleaned unless one of the gas guide plates is removed. Moreover, since two gas guide plates 2 and 3 are used, the number of parts required in the apparatus is high, and the apparatus is more expensive. Particularly in the case of Conventional Example 1, since the specially shaped ducts 5 of the guide plates are designed so as to be wider toward the nozzle 1 and narrower away from the nozzle 1, the cost of the apparatus is greatly increased.